1. Field of the Invention
The present invention relates to a focus detection apparatus.
2. Description of the Related Art
As image capturing apparatuses represented by a digital camera and a video camera prevail, there has been an increasing demand for higher quality and downsizing of the image capturing apparatuses. More specifically, it has been desired to achieve higher precision and downsizing of a focus detection apparatus which detects the focus state of an imaging lens (imaging optical system) of an image capturing apparatus. In recent years, a focus detection apparatus which utilizes a TTL phase difference detection method for detecting the focus state of the imaging lens based on a relative positional relationship between a plurality of optical images formed by light beams passing through a plurality of regions obtained by dividing the pupil of the imaging lens is becoming the mainstream.
Such a focus detection apparatus described above forms a pair of images on a pair of light-receiving element arrays using a pair of lens portions formed on the incident surface of a secondary imaging lens, and a pair of prism portions formed on the exit surface. As an imaging lens goes out of focus, the pair of images move in a correlation direction as a direction in which a pair of openings are aligned. It is, therefore, possible to provide a focus detection apparatus that can detect a focus in a wide range within a photographing frame by arranging a plurality of focus detection regions in a direction perpendicular to the correlation direction. In, for example, Japanese Patent Laid-Open No. 2007-139935, a plurality of focus detection regions are arranged in the horizontal and vertical directions with respect to a photographing frame.
Japanese Patent Laid-Open No. 11-281877 describes a focus position detection apparatus, in which the first and second cross sensors which form an angle of about 45° with respect to each other are provided in the center of a frame.
As in Japanese Patent Laid-Open No. 2007-139935, arranging a plurality of focus detection regions in a direction perpendicular to the correlation direction as a direction in which the pair of openings are aligned has been conventionally considered. However, arranging a plurality of focus detection regions in an oblique direction as described in Japanese Patent Laid-Open No. 11-281877 has not been considered.
With reference to Japanese Patent Laid-Open No. 2007-139935, to densely arrange a plurality of focus detection regions in an oblique direction as described in Japanese Patent Laid-Open No. 11-281877, a plurality of focus detection regions are preferably arranged in a direction perpendicular to the correlation direction.
On the other hand, objects such as buildings, artificial objects, or eyebrows often have contrast in the horizontal or vertical direction. It is, therefore, easier to recognize the contrast of an object when a focus detection region extends in the horizontal or vertical direction as compared with an oblique direction. A field mask limiting a light beam for focus detection generally has a shape suitable for focus detection in the horizontal or vertical direction.